Divided products are understood to be ail types of products divided into particles, grains, crystals, etc., having a low or high granulometry. In the document presented here, the term xe2x80x9cpulverulentxe2x80x9d specifies this type of product.
The invention presented here involves a device that allows the automated metering of specified quantities of solid pulverulent products having very diverse physical characteristics. The metering of a powder in a specified quantity requires removing it from a storage container, transporting it until a discharge point, discharging it, generally into a container placed on a precision scales, and stopping the flow when the desired quantity has been reached. Depending on the physical characteristics of the powder to be metered, the difficulty of the operation remains especially in the extraction and the transport or in attaining the precision of the dosage at the end of the operation.
Known from the French invention patent number 94/09835, granted to the applicant, is a metering device for powder that implements, at the bottom of a container in which the powder to be metered is mixed by stirrers, a horizontal tube that adjoins the container, pierced at the bottom at one of its ends by an opening and in which is placed a loader driven in rotation, which consists of a shaft carrying a blade that forms a helical spring. This loader acts like an Archimedean screw, and its behavior in the case it becomes jammed encourages the backblowing of the horizontal tube.
Also known from the French patent application number 95/06081 in the name of the applicant is an additional device characterized essentially by the presence at the level of the outlet opening of the powder to be dosed. In the configuration described in this patent, the transporter shaft extends downstream from the opening and comes to enter into a bearing that is united with the structure of the device. According to this configuration, the disc always contains a pierced hole that passes through in the middle, by which it is mounted with the possibility for sliding on the downstream part of the shaft. The disc, the edge of which contains a chamfer relative to the shifting mechanism, is drawn towards the opening in order to completely block it, by a spring mounted around the downstream part of the shaft. This disc, under the pressure of the powder transported in the tube, is likely to become displaced on the downstream part of the screw, contrary to the action exerted by the spring. Thus, under the action of the pressure, the opening is more or less cleared and some of the powder can get out of the tube. This device makes it possible to create many small meterings, where the disc allows, when the flow rate oft he powder is low, only the flow of the finest grains. A particular embodiment mode of this device allows the mixing of the powder in the tank by means of a helical spring set in rotation above the screw or the shifting spring.
All of these devices have some disadvantages, however:
the extraction of powders from the storage tank is sometimes difficult, as a function of their physical characteristics: the mixing device can prove to be insufficient in certain cases.
the dimensioning of the spring connected to the blocking disc is difficult: thus, as a function of the physical characteristics of the powder, it can either limit the flow rate, or close the tube in an incomplete manner.
The invention presented here has the goal of correcting these disadvantages.
For this purpose, the device for metering pulverulent products in dosed quantities is essentially characterized in that it contains a tank for storage of the powder to be let out in dosed quantities, a tubular duct that reaches into the tank in the lower part of the tank, where the tubular duct accommodates on the inside a component for metering the pulverulent product in the tank and for transporting it from a loading opening that the duct makes in the tank to an opening for discharging the pulverulent product, which the duct has on the outside of the tank, where the discharge opening is combined with a blocking component that can be positioned upon command and kept either in a position of total unobstruction of the opening or in a position of blocking the opening by which an annular interval exists between the outline of the opening and the outline of the blocking component, the width of the annular interval being on the same order of magnitude as the size of each grain of the pulverulent product.
It is understandable that the position of total unobstruction allows a maximum flow rate of the pulverulent product across the outlet opening. On the other hand, the blocking position leads to a very low flow rate allowing a great precision in the quantity of the pulverulent product delivered. The low width of the annular interval between the outlet opening and the blocking component creates a sizeable head loss and largely slows down the flow of the product which becomes compressed behind and against the blocking component under the action of the pressure forces resulting from the movement of the transport component. These pressure forces have the effect of forcing the passage of a low quantity of product across the annular interval. The grains of a size slightly larger than the size of the interval either do not pass or are cut and divided during their passage. With these characteristics, experience shows that it is possible to obtain a precision in the dosage on the order of a milligram, which permits the use of this device for automatic and repeat dosage of pharmaceutical compositions and other compositions requiring high degrees of precision.
According to another characteristic of the invention, the metering and transport component consists of a shaft placed along a central longitudinal axis of the duct and of at least one pressure instrument affixed to the shaft and making several successive turns around the shaft, while the metering and transport component is mounted by its shaft so that it is mobile in rotation on two interdependent bearings at the ends of the duct, one of which is outside the tank and the other is inside, the metering component being driven in rotation upon command by its shaft, by a motor element around the central longitudinal geometric axis of the shaft.
This device has the advantage of simplicity and makes it possible, in controlling and adjusting the speed of the rotation of the metering component, to adjust the value of the flow rate of the discharged product. In addition, it is possible by driving the component in rotation in the opposite direction, to reduce the pulverulent product contained in the duct in the tank, and possibly avoid any interference flow of the product.
According to another characteristic of the invention, the blocking component is perpendicular to the geometric axis of rotation of the shaft and can be displaced in translation along the shaft and between the position of total unobstruction and the position of total blocking.
According to another characteristic of the invention, the blocking component is fixed in translation to the shaft and the shaft is mounted in a manner mobile in translation along the geometric axis of rotation in the translational guide bearings.
According to another characteristic of the invention, the shaft of the metering component, at the level of its bearing outside the tank, is extended beyond the tank in order to accommodate a component for coupling to a motor assembly for driving in rotation and translation. The advantage of these technical characteristics lies essentially in the fact that only one and the same motor assembly is used to activate the shaft in rotation and translation.
According to another characteristic of the invention, the metering device of the pulverulent products is equipped in the tank with a device for mixing and breaking up clumps of the pulverulent product.
This device prevents the aggregation of the product in the tank and ensures, consequently, the regular supply of pulverulent product to the metering and transport component. The invention presented here also has the object of a system for automatic dosage of pulverulent products characterized essentially in that it contains at least one device according to the invention.
According to another characteristic, the system is made up of several devices put together in at least one rectilinear or circular row, towards which is moved a motorized rotating meter element, carrying the motor assembly for setting into rotation and translation the shaft of the metering and transport component, as well as a weighing balance and a receiving container for pulverulent product installed on the weighing balance.
According to another characteristic, the motor assembly includes of an electric motor on the rotary output shaft of which is fixed, as much in translation as in rotation, a toothed wheel designed to be in mesh with the coupling component having a toothed pinion.
According to another characteristic, the motor assembly is provided with a horizontal mechanical plate mounted to slide on slide rails that are perpendicular or radial to the row of devices, and with a second motor for displacing the mechanical plate along the slide rails and to move the toothed wheel above the pinion or even to detach it from the pinion.
According to another characteristic, the toothed wheel is made in the shape of a circular sector and has a rectilinear clearance hole by which it is positioned above the pinion by displacement of the mechanical plate before being engaged with the pinion and the wheel is equipped on both sides of its toothed zone with two lateral sides in the shape of a circular sector, which by rotation of the wheel come to be located on both sides of the toothed pinion. Lastly, according to another characteristic, the rotating element of the meter carries a lower clamping jaw that is moved by an ascending movement for engagement and a descending movement for disengagement by an actuating drive. The lower jaw comes to end in a forked shape that comes at the end of the path of the ascending movement to be positioned behind the toothed pinion around the shaft. The sliding rails of the mechanical plate are mounted on an appropriate support mounted on the vertical sliding rails and set in motion in vertical translation by a motor element.